Stroke is a leading cause of high mortality and long-term disability in the United States. Stroke is associated with the over-production of misfolded/aggregating proteins. However, the role of aberrant protein clearance on the outcome of ischemic stroke remains far from being understood. The ubiquitin proteasome system (UPS) plays a critical role in the removal of abnormal proteins. The UPS is regulated by a number of factors but recent data indicate that the proteasome-associated deubiquitinating enzymes (DUBs) play an important role in regulating proteasome activity. USP14 is the DUB that is reversibly associated with the proteasome and modulates proteasome activity. Recently, a USP14-specific small molecule inhibitor, IU1, was identified (Lee et al. 2010, Nature 467:179-184). In cell culture, IU1 accelerates the clearance of oxidized proteins and imparts a resistance effect on oxidative stress-induced cell death. These results suggest that IU1 may be a potential drug that can be used for treating cerebral ischemia/reperfusion-caused disorders. However, this has not been tested in ischemic stroke animal models. In this project, we hypothesize that peripheral administration of IU1 in mice will attenuate neuronal death and promote structural repair and functional recovery following transient cerebral ischemic stroke. To test this hypothesis, the following specific aims will be pursued. 1. Examine whether IU1, a DUB inhibitor, enhances the degradation of a surrogate proteasome substrate in a proteasome function reporter mouse model with or without ischemia/reperfusion. 2. Determine whether peripheral administration of IU1 protects neurons from transient focal cerebral ischemia-caused neuronal injury.